It is acknowledged that knitting of a fracture is impossible or almost impossible if there are movements of notable amplitude in the direction of the shear at the fracture surface. On the other hand, the knitting occurs in a manner that is all the more favorable if variable and not excessive pressure stresses are applied perpendicular to the fracture. Presently available methods of osteosynthesis are far from achieving an ideal bone fastening which prevents shears and favors variable, non excessive pressure stresses perpendicular to the fracture.
Very diagrammatically it is possible to contrast two groups of known means of bone fastening: rigid fastening means, or heavy osteosynthesis, and flexible fastening means, or light osteosynthesis. Fastening means can be called heavy osteosynthesis which consists of bulky equipment such as screwed plates or pinnings after boring These means provide completely rigid immobilizations of the fracture zone. This rigidity indeed prevents shearing of the fractured zone which knits in almost all cases, but this rigidity does not permit, or only slightly permits, variable pressures perpendicular to the fracture zone favorable to knitting, so that the latter often occurs with extended periods, even very extended periods, in relation to the optimal possibilities of bone knitting. Further, the use of these means requires more or less devitalizing the tissues, and especially the bone, which entails a number of risks, the most serious of which is the risk of extensive septic contamination, at times serious, and often difficult to heal. Further, the removal of the osteosynthesis equipment, of course, is necessary; it is generally done about eighteen months after placement, to avoid lasting modifications of the bone physiology induced by the greatness of the rigidity of the equipment, consisting of spongialization or extensive osteoporosis of the bone thus relieved of its physiological function.
Light osteosynthesis means comprise small pins and standard clips some of which comprise two approximately parallel lateral rods, connected together by a bridge-forming straight or angular central part, and whose median axis is located in the same plane as that of the median axes of the lateral rods. These known means of light osteosynthesis offer the advantage of allowing the manifestation, at the fracture focus, of compressions induced by contractions of the skeletal muscles of the limb. Unfortunately, by themselves, they do not always satisfactorily prevent the shear movements which are particularly unfavorable to knitting and, when they are used alone, they entail risks of pseudoarthrosis. When supplementary holding means are added to them, such as a plaster cast, this is done to the detriment of the comfort of the patient and, as a general rule, cannot constitute an ideal immobilization of the fracture zones in the shear direction.